Electrostatic chuck bonded to base with a bond layer and method

ABSTRACT

An electrostatic chuck for holding a substrate has an electrostatic member having a dielectric covering an electrode that is chargeable to electrostatically hold the substrate. The bond layer has a metal layer that is infiltrated or brazed between the electrostatic member and the base. The base may be a composite of a ceramic and metal, the composite having a coefficient of thermal expansion within about ±30% of a coefficient of thermal expansion of the electrostatic member. The base may also have a heater.

CROSS REFERENCE

[0001] This application is a divisional of U.S. patent application Ser.No. 09/307,214, filed on May 7, 1999, titled Electrostatic Chuck HavingHeater and Method by Wang, et al. which is incorporated herein byreference in its entirety.

BACKGROUND

[0002] The present invention relates to an electrostatic chuck forholding a substrate in a chamber.

[0003] Electrostatic chucks, which use electrostatic attraction forcesto hold a substrate, have several advantages over mechanical and vacuumchucks. For example, electrostatic chucks reduce stress-induced crackscaused by mechanical clamps, allow processing of a larger portion of thesubstrate, and can be used in processes conducted at low pressures. Atypical electrostatic chuck comprises an electrode covered by adielectric. When the electrode is electrically charged, an opposingelectrostatic charge accumulates in the substrate and the resultantelectrostatic force holds the substrate onto the electrostatic chuck.Once the substrate is firmly held on the chuck, a plasma of gas is usedto process the substrate.

[0004] Certain newly developed plasma processes for the fabrication ofintegrated circuits are often performed at high temperatures and inhighly erosive gases. For example, processes for etching copper orplatinum are conducted at temperatures of from 250 to 600° C., comparedto temperatures of 100 to 200° C. for etching aluminum. The hightemperatures and erosive gases thermally degrade the materials used tofabricate the chucks. The high temperature requirement is met by ceramicmaterials, such as aluminum oxide (Al₂O₃) or aluminum nitride (AIN).However, it is difficult to attach the ceramic chuck to chambercomponents which are typically made from metal because the difference inthermal expansion coefficients of the ceramic and metal can result inthermal and mechanical stresses that can cause the ceramic to fractureor chip. It is desirable to have a system for fastening a ceramic chuckto a chamber without causing excessive thermal stresses between thechuck and the chamber.

[0005] In addition, the newly developed processes often require thesubstrate on the electrostatic chuck to be heated to temperatures higherthan those provided by the heat load of the plasma. The hightemperatures can be obtained by using a heater, for example, thesubstrate can be heated by infrared radiation from heat lamps providedoutside the chamber. However, it is difficult to pass infrared radiationthrough the aluminum oxide or metal walls of the chamber. In anotherapproach, as described in U.S. Pat. No. 5,280,156, the electrostaticchuck comprises a ceramic dielectric having both the electrode and theheater embedded therein. However, operating the embedded heater at highpower levels can cause the ceramic dielectric covering the electrode tomicrocrack from the thermal stresses generated by differences in thermalexpansion between the ceramic, electrode, and heater. Thus, there is aneed for an electrostatic chuck that can be heated to high temperatureswithout damaging the chuck.

[0006] In certain processes, it is also desirable to rapidly cool thesubstrate in order to maintain the substrate in a narrow range oftemperatures, especially for etching interconnect lines that have verysmall dimensions and are positioned close together. However, temperaturefluctuations occur in high power plasmas due to variations in thecoupling of RF energy and plasma ion densities across the substrate.These temperature fluctuations can cause rapid increases or decreases inthe temperature of the substrate. Also, variations in heat transferrates between the substrate and chuck can arise from the non-uniformthermal impedances of the interfaces between the substrate, chuck, andchamber. Thus, it is desirable to have an electrostatic chuck that canrapidly cool the substrate to more closely control the temperature ofthe substrate.

[0007] Another problem that frequently arises with conventionalelectrostatic chucks is the difficulty in forming a secure electricalconnection between the electrode of the electrostatic chuck and anelectrical connector that conducts a voltage to the electrode from aterminal in the chamber. Conventional electrical connectors have springbiased contacts which can oxidize and form poor electrical connectionsto the electrode. Moreover, electrical connections formed by solderingor brazing the electrical connector to the electrode often result inweak joints that can break from thermal or mechanical stresses. Thus, itis desirable to have an electrostatic chuck with a secure and reliableelectrical connection between the electrode and electrical connector.

[0008] Yet another problem frequently arises from the vacuum sealbetween the electrostatic chuck and the surface of the chamber,especially for high temperature processes. Typically, fluid, gas, andelectrical lines extend to the electrostatic chuck through vacuum sealedfeedthroughs in the chamber. In conventional chambers, the feedthroughsare vacuum sealed by polymer O-rings that are positioned in groovesextending around their circumference. However, the polymer O-rings oftenlose their compliance and resilience at high temperatures making itdifficult to maintain the integrity of the vacuum seal.

[0009] Accordingly, there is a need for an electrostatic chuck that canbe operated at high temperatures without excessive thermal or mechanicaldegradation. There is also a need for an electrostatic chuck that canheat the substrate to higher temperatures than those provided by theheat load of the plasma. There is also a need for an electrostatic chuckhaving a uniform and low thermal impedance to transfer heat to and fromthe substrate to allow rapidly heating or cooling of the substrate.There is a further need for an electrostatic chuck having a secure andreliable connection between its electrode and electrical connector.There is also a need for degradation resistant vacuum seal between theelectrostatic chuck and chamber.

SUMMARY

[0010] An electrostatic chuck for holding a substrate, the electrostaticchuck comprising an electrostatic member comprising a dielectriccovering an electrode that is chargeable to electrostatically hold thesubstrate, and a base bonded to the electrostatic member by a bondlayer, the base comprising a heater capable of raising the temperatureof a substrate held on the electrostatic member by at least about 100°C.

[0011] A method of fabricating an electrostatic chuck for holding asubstrate, the method comprising the steps of:

[0012] (a) forming an electrostatic member comprising a dielectriccovering an electrode that is chargeable to electrostatically hold thesubstrate;

[0013] (b) forming a base comprising a heater capable of raising thetemperature of a substrate held on the electrostatic member by at leastabout 100° C.; and

[0014] (c) bonding the base to the electrostatic member by a bond layer.

[0015] An electrostatic chuck for holding a substrate, the electrostaticchuck comprising an electrostatic member comprising a dielectriccovering an electrode that is chargeable to electrostatically hold thesubstrate, and a base bonded to the electrostatic member by a bondlayer, the base comprising a composite of a ceramic and metal, thecomposite comprising a coefficient of thermal expansion within about±30% of a coefficient of thermal expansion of the electrostatic member.

[0016] A method of fabricating an electrostatic chuck for holding asubstrate, the method comprising the steps of:

[0017] (a) forming an electrostatic member comprising a dielectriccovering an electrode that is chargeable to electrostatically hold thesubstrate;

[0018] (b) forming a base comprising a composite of a ceramic and metal,the composite comprising a coefficient of thermal expansion within about±30% of a coefficient of thermal expansion of the electrostatic member;and

[0019] (c) bonding the base to the electrostatic member by a bond layer.

DRAWINGS

[0020] These features, aspects, and advantages of the present inventionwill become better understood with regard to the following description,appended claims, and accompanying drawings which illustrate examples ofthe invention, where:

[0021]FIG. 1 is a schematic sectional side view of a chamber showing anelectrostatic chuck according to the present invention;

[0022]FIG. 2 is a schematic sectional side view of an electrostaticchuck having a base comprising channels for circulating heat transferfluid;

[0023]FIG. 3 is a graph showing the change in the coefficient of thermalexpansion of a base for increasing volume fraction of ceramic in thebase;

[0024]FIG. 4a is a schematic sectional side view of an electrostaticchuck comprising a base comprising two components, namely a central diskand an annular ring;

[0025]FIG. 4b is a schematic top plan view of the base of FIG. 4ashowing the central disk having carbon fibers oriented in at least twoorthogonal directions;

[0026]FIG. 5 is a schematic sectional side view of an electrostaticmember, a base, and a support having channels for circulating heattransfer fluid;

[0027]FIG. 6 is a schematic sectional side view of another version of anelectrostatic chuck;

[0028]FIG. 7a is a schematic sectional side view of an electrostaticmember, a base, and a support comprising a cavity that thermallyisolates the base from a surface of a chamber;

[0029]FIG. 7b is a schematic sectional side view of another embodimentof the support comprising a cavity having a trapezoidal cross-section;

[0030]FIG. 7c is a schematic sectional side view of yet anotherembodiment of the support comprising a channel having a rectangularcross-section, a gas inlet for supplying gas to the channel, and a gasoutlet for removing gas from the channel;

[0031]FIG. 8a is a schematic sectional side view of a portion of anelectrostatic chuck showing an electrode, electrical connector, and adisc of conducting material therebetween; and

[0032]FIG. 8b shows the electrostatic chuck of FIG. 8a after the disc ofconducting material being melted and cooled to electrically connect theelectrode to the electrical connector.

DESCRIPTION

[0033] An exemplary chamber 25 for processing a substrate 30, such as asemiconductor wafer, is illustrated in FIG. 1. The chamber 25 comprisesa ceiling 35, sidewalls 40, and a lower surface 50 on which rests anelectrostatic chuck 55 that is used to securely hold the substrate 30during processing. The chamber 25 further comprises a process gasdistributor 60 having one or more holes 65 for introducing process gasfrom a process gas supply 70 into the chamber 25. An exhaust system 75is used to exhaust spent gas and gaseous byproducts from the chamber 25and to control the pressure of gas in the chamber 25. The exhaust system75 typically comprises an exhaust conduit having a throttle valve 80,and a plurality of pumps 85 such as roughing pumps and turbomolecularpumps. The process gas is energized by coupling RF energy to the processgas in the chamber 25 (as shown) or the process gas can be energized bymicrowaves in a remote chamber adjacent to the chamber 25 (not shown).In the exemplary chamber 25, the process gas is energized to form aplasma by applying an RF current to an inductor coil 95 adjacent to theceiling 35 to inductively couple RF energy to the gas in the chamber 25.The frequency of the RF energy applied to the inductor coil 95 istypically from about 50 KHz to about 60 MHz, and more typically about13.56 MHz.

[0034] The electrostatic chuck 55 includes an electrostatic member 100comprising an electrode 105 covered by or embedded in a dielectric 115,and having a receiving surface 120 for receiving the substrate 30. Aheat transfer gas, typically helium, is supplied from a heat transfergas supply 125 and through a conduit 130 to grooves 135 in the receivingsurface 120 to enhance heat transfer rates between the substrate 30 andthe electrostatic chuck 55. The dielectric 115 comprises a material thatallows RF energy to be coupled from the electrode 105 to the plasma, andthat also serves as an insulator that allows a DC voltage applied to theelectrode 105 to electrostatically hold the substrate 30. The electrode105 of the electrostatic member 100 comprises a single electricalconductor for monopolar operation (as shown in FIG. 1) or two moreelectrically isolated conductors for bipolar operation (as shown in FIG.2). In a monopolar chuck 55, a voltage applied to the electrode 105causes electrostatic charges to accumulate in the electrode 105 or inthe dielectric 115. Energized process gas above the substrate 30provides electrically charged species having opposing polarity whichaccumulate in the substrate 30 resulting in an attractive electrostaticforces that holds the substrate 30 to the receiving surface 120 of theelectrostatic chuck 55. In a bipolar chuck 55, at least two electrodes105 a,b are maintained at different electric potentials, therebyinducing electrostatic charges in the substrate 30 that hold it to thereceiving surface 120. An electrical connector 140 electrically connectsthe electrode 105 to a voltage supply 145 to provide desired voltage tothe electrode 105 to electrostatically hold the substrate 30.Optionally, the voltage supply 145 also provides an RF voltage to theelectrode 105 to energize and accelerate the plasma species toward thesubstrate 30 by capacitively coupling RF energy to the plasma.

[0035] To operate the electrostatic chuck 55, the chamber 25 isevacuated and maintained at a sub-atmospheric pressure. A lift pinassembly 155 comprises lift pins 160 a,b that are elevated through holes165 a,b in the electrostatic chuck 55 by a pneumatic lift mechanism 170.A robot arm (not shown) places the substrate 30 on the lift pins 160a,b, and the pneumatic lift mechanism 170 lowers the substrate 30 ontothe receiving surface 120. After the substrate 30 is placed on theelectrostatic chuck 55, the electrode 105 of the electrostatic chuck iselectrically biased with respect to the substrate 30 by the voltagesupply 145 to electrostatically hold the substrate 30. The voltagesupply 145 provides a DC voltage of about 1000 to 3000 volts to theelectrode 105. Helium, is supplied through the conduits 130 to grooves135 in the receiving surface 120 at the interface between the substrate30 and the electrostatic chuck 55 to thermally couple the substrate 30to the electrostatic chuck 55. Thereafter, an energized process gas isprovided in the chamber 25 to process the substrate 30 held on thesubstrate. On completion of the process, the pneumatic lift mechanism170 raises the lift pins 160 to raise the substrate 30 off the receivingsurface 120, allowing the substrate 30 to be removed by the robotic arm(not shown). Before raising the lift pins 160, the substrate 30 iselectrically decoupled or de-chucked by dissipating the residualelectrical charges holding the substrate 30 to the electrostatic chuck55. This is accomplished, after the voltage to the electrode 105 isturned off, by grounding the electrode 105 or maintaining a plasma atanother power level to provide a path to electrical ground for theelectrostatic charges accumulated in the substrate 30.

[0036] Particular aspects of the electrostatic chuck 55 and the systemfor supporting and holding the chuck 55 in the chamber 25 will now bedescribed. As shown in FIG. 2, generally, the electrostatic member 100of the electrostatic chuck 55 is supported by a base 175 that is shapedand sized to match the electrostatic member 100 to promote efficientheat transfer across the interfaces therebetween. The base 175 cancomprise channels 180 through which heat transfer fluid is circulated toraise or lower the temperature of a substrate 30 held on the receivingsurface 120 of the electrostatic member 100. This enables thetemperature of the substrate to be precisely controlled to provide moreuniform processing. A support 190 can also be provided to support thebase 175, and the support 190 rests on the surface 50 of the chamber 25.The base 175 and the support 190 secure the electrostatic chuck 55 tothe chamber 25, provide reduced levels of thermal expansion mismatch,and provide more uniform heat transfer rates across the interfacestherebetween.

[0037] Base

[0038] In one aspect of the present invention, the base 175 forsupporting the electrostatic member 100 is fabricated to have acoefficient of thermal expansion that is sufficiently close to that ofthe electrostatic member 100 to reduce thermal expansion stresses thatwould otherwise cause the electrostatic member 100 to separate from thebase 175. In this version, the base 175 comprises a composite materialhaving a tailored coefficient of thermal expansion. The composite base175 is composed of a plurality of materials, for example, a mixture oftwo or more materials, including a first material and a second material,the volume fraction of the two materials being selected so that the base175 has a coefficient of thermal expansion that is within about ±30% ofa coefficient of thermal expansion of the electrostatic member 100.Preferably, the first material is a ceramic and the second material is ametal to provide a composite material having some ductility andincreased fracture toughness.

[0039] In one version, the base 175 comprises a porous ceramicinfiltrated with molten metal. The metal fills all the pores in theceramic when they are open and interconnected to one another, or onlysome of the pores at the surface of the porous ceramic, when the poresare not interconnected throughout the structure. The coefficient ofthermal expansion of a base 175 comprising a porous ceramic infiltratedwith a molten metal is tailored by varying the volume fraction of theceramic to the metal. FIG. 3 shows the change in the coefficient ofthermal expansion of the base 175 for increasing volume fraction ofceramic based on the formula

α_(b)=(α_(m) V _(m) E _(m)+α_(c) V _(c) E _(c))/(V _(m) E _(m) +V _(c) E_(c)),

[0040] where α_(b) is the CTE for the base 175,

[0041] α_(m) V_(m), and E_(m), respectively, are the CTE, volumefraction, and Young's modulus for the metal, and

[0042] α_(c), V_(c), and E_(c), respectively, are the CTE, volumefraction, and Young's modulus for the ceramic material.

[0043] For example, when the electrostatic member 100 comprisesdielectric 115 composed of aluminum nitride, preferably, the base 175comprises a coefficient of thermal expansion of from about 3 to about 15ppm/° C., and more preferably from about 4 to about 10 ppm/° C., toprovide a suitable level of CTE matching between the base 175 and theelectrostatic member 100.

[0044] The ceramic material is capable of withstanding temperatures ofat least about 400° C. and more preferably at least about 600° C.Suitable ceramic materials include one or more of aluminum oxide,aluminum nitride, boron carbide, carbon, cordierite, mullite, siliconcarbide, silicon nitride, silicon dioxide and zirconium oxide. Suitablemetals for infiltrating the porous ceramic include aluminum, copper,iron, molybdenum, titanium, tungsten or alloys thereof. The porousceramic preferably comprises a pore volume of from about 20 to about 80volume % to provide a sufficiently large volume for metal infiltration.In a preferred embodiment, the base 175 comprises silicon carbide (SiC)infiltrated with aluminum (Al), the volume fraction of the ceramic tothe metal being from about 20 to about 80 volume %. As the volumefraction of ceramic to metal changes, so does the thermal and mechanicalproperties of the base 175. For example, referring to Table I, it isseen that for a base 175 comprising a silicon carbide infiltrated byaluminum, the coefficient of thermal expansion and tensile strength ofthe base 175 decreases as the volume fraction of ceramic to metalincreases, while the thermal conductivity remains constant. TABLE IVOLUME FRACTION OF CERAMIC TO METAL (%) 63% SiC 65% SiC 70% SiC CTE(ppm/° C.) 7.9-8.1 7.2-7.7 5.7-7.0 TENSILE STRENGTH (GPa) 249 205 192THERMAL CONDUCTIVITY 175 175 175 (W/mk)

[0045] In another version, the base 175 further comprises carbon fibers200 that are oriented to provide a coefficient of thermal expansion thatmatches that of the ceramic dielectric 115. For example, as shown inFIG. 4b, the base 175 can comprise a first set of carbon fibers 200 aoriented parallel to a first axis of orientation 205 a, and a second setof carbon fibers 200 b oriented parallel to a second axis of orientation205 b that is at an angle (p with respect to the first axis oforientation 205 a. Preferably, the orientation and volume fraction ofcarbon fibers 200 are selected so that the base 175 has a coefficient ofthermal expansion that is substantially isotropic in the same plane asthat of the processing surface of the substrate 30 to minimize thermalexpansion stresses on the electrostatic member 100. More preferably, thebase 175 comprises carbon fibers 200 that are oriented in a plurality oforthogonal directions. The carbon fibers 200 oriented in a particulardirection expand in the direction parallel to their axis 205 a or 205 b.Thus, orienting the carbon fibers 200 in orthogonal directions within asingle plane tends to substantially equalize their thermal expansion intwo or more different axial directions within the same plane to providea more uniform coefficient of thermal expansion within the plane. Inaddition, the base 175 can comprise carbon fibers 200 oriented in aplurality of directions within the single plane—for example, at 20, 45,or 60° intervals—to provide an even more anisotropic thermal expansionwithin the plane.

[0046] The coefficient of thermal expansion of the base 175 can befurther tailored to match that of the electrostatic member 100 byforming a base 175 comprising a hybrid or plurality of component membersthat each have a different coefficient of thermal expansion. The overallcoefficient of thermal expansion of the base 175 depends on theexpansion coefficient of the individual component members and on theirlinear dimensions, α_(b)=(α₁D₁+α₂ (D₂−D₁))/D₂,

[0047] where

[0048] α_(b) is the overall coefficient of thermal expansion of thehybrid composite base,

[0049] α, and α₂ are CTEs of individual component members, and

[0050] D₁ and D₂ are linear dimensions of individual component members.

[0051] Preferably, the ratio of the linear dimensions of the componentmembers are selected so that the coefficient of thermal expansion of thebase 175 is within about ±30% of the CTE of the electrostatic member100. The components of the base 175 are shaped and sized to cooperate toachieve multifunctional properties. For example, as shown in FIGS. 4aand 4 b, the base 175 can comprise two components 210, 215 havingcircular symmetry to one another to provide different coefficients ofthermal expansion at the center 220 and peripheral edge 225 of theoverlying electrostatic chuck 55. In this version, the base 175comprises a disk 210 surrounded by an annular ring 215, each having adifferent average coefficient of thermal expansion. Both the disk 210and the annular ring 215 are made up of a porous ceramic infiltratedwith metal as described above. However, the volume fraction of theceramic to metal is different in each, and one or more can comprisecarbon fibers 200 in differing volume fractions. FIG. 4b shows a base175 having a disk 210 comprising a composite material containing carbonfibers 200 that are oriented in at least two orthogonal directions toprovide a more uniform expansion coefficient in a plane parallel to theplane of the substrate 30. The disk 210 is surrounded by an annular ring215 made of porous silicon carbide infiltrated with metal.

[0052] In still another version, shown in FIG. 5, the base 175 comprisesa thermally insulating material such as a ceramic member that thermallyinsulates the electrostatic chuck 55 from the surface 50 of the chamber25 (not shown) or the support 190. In this embodiment, the support 190further comprises channels 230 for circulating heat transfer fluidtherethrough. The base 175 serves as an interposer member lying betweenthe electrostatic chuck 55 and the surface 50 of the chamber 25 orbetween the electrostatic chuck 55 and the support 190. This reduces theheat escaping from the electrostatic chuck 55 via heat conductionthrough the surface 50 of the chamber 25 to maintain the substrate 30 athigher temperatures. In addition, the base 175 enables the electrostaticchuck 55 to form a gas tight seal with an underlying support 190 orsurface 50 of the chamber 25 by use of a conventional polymer O-ring240. The O-ring 240 is typically made from a polymer, such aspolyethylene, polyurethane, polycarbonate, polystyrene, nylon,polypropylene, polyvinylchloride, fluoroethylene polymers, or silicone,all of which are susceptible to damage by high temperatures. Forexample, temperatures of over 200° C. can cause a polyimide O-ring tolose its resilience and its ability to form a seal. Because of its lowthermal conductivity, the base 175 provides a temperature differentialsufficient high to enable the electrostatic chuck 55 to be vacuum sealedto the support 190 by an O-ring 240 without degradation of the O-ring.Preferably, the base 175 comprises a thermal conductivity sufficientlylow to provide a temperature differential of at least about 100° C.between the receiving surface 120 of the electrostatic chuck 55 and thebottom surface 50 of the chamber 25 or the support 190. More preferably,the base 175 comprises a thermal conductivity of less than about 6 W/mK.

[0053] In the embodiment shown in FIG. 5, the base 175 is made from aceramic material, such as for example, aluminum oxide, aluminum nitride,boron carbide, carbon, cordierite, mullite, silicon carbide, siliconnitride, silicon dioxide and zirconium oxide. Of these mullite andcordierite are preferred, because they have thermal conductivities ofless than about 6 W/mK and coefficients of thermal expansion of about 5ppm/° C. which is very close to that of the dielectric 115 of theelectrostatic chuck 55. Both mullite and cordierite also have a highresistance to thermal shock. Thermal shock results from the thermalstress caused by rapid heating and cooling and it can cause microcracksto occur in a material which lead to structural failure. Thus, a highresistance to failure from thermal shock is desirable for a base 175that is alternately heated and cooled by the support 190. In addition tohaving a high resistance to thermal shock, both mullite and cordieritehave a high resistance to erosion by energized process gases making themuseful in processes using reactive process gases, such as fluorine.

[0054] Bond Layer

[0055] In another aspect of the present invention, the base 175 isbonded or joined to the electrostatic member 100 by a bond layer 250made from a material having high thermal conductivity, as illustrated inFIG. 6. The bond layer 250 can comprise, for example a metal, such asaluminum, copper, iron, molybdenum, titanium, tungsten or alloysthereof, to provide more uniform heat transfer rates across the bondlayer 250 which is desirable to provide more uniform processing. Thebond layer 250 eliminates use of bolts for securing the electrostaticmember 100 to the base 175 and consequently reduces mechanical stresseson the electrostatic chuck 55. Also, the bond layer 250 has ahomogeneous composition that provides more uniform heat transfer ratesacross the substrate 30, and reduces the differences in thermalimpedances that occur at the interface between the base 175 and theelectrostatic member 100. Differences in thermal impedances can occur,for example, at the interface between the base 175 and the electrostaticmember 100 that has a rough surface with gaps and non-contact areas thathave a high thermal impedance relative to regions having smoothsurfaces. The bond layer 250 is especially desirable for anelectrostatic chuck 55 comprising a ceramic dielectric 115 which has alower surface 252 that forms the interface between the electrostaticmember 100 and the base 175 that often contains microscopic gaps andfissures (not shown). In conventional electrostatic chucks, these gapsand fissures can create a thermal barrier between the electrostaticmember 100 and the base 175. In contrast, in an electrostatic chuck 55according to the present invention, the bond layer 250 fills the gapsand fissures to provide a smooth surface to provide more controllableand uniform heat transfer rates.

[0056] Preferably, the bond layer 250 is ductile and compliant toprovide an interface that absorbs the thermal stresses arising from thethermal expansion mismatch between the dielectric 115 of theelectrostatic member 100 and the base 175 without damaging theelectrostatic chuck. While a bonded joint provides uniform heat transferrates, it is often difficult for a bonded joint to withstand the thermalstresses arising from differences in thermal expansion coefficients ofdissimilar materials, such as the electrostatic member 100 and the base175. A bond layer 250 according to the present invention, made from aductile and compliant material can flex and absorb thermal stresses thatarise from the difference in thermal expansion coefficients of theelectrostatic member 100 and the base 175. The bond layer 250 could alsobe made from a polymer which is compliant and able to absorb thermalstresses. However, conventional polymer materials are often eroded byerosive plasma and process gases, and thus it is preferred to use acompliant metal to form the bond layer 250. Also, the bond layer made ofmetal generally has a higher thermal conductivity than a bond layer madeof polymer.

[0057] Preferably, the bond layer 250 is made by infiltrating moltenmetal into the interface between the dielectric 115 and the base 175.For example, a base 175 comprising a composite of porous ceramic andmetal can be bonded to the dielectric 115 of the electrostatic member100 by a bond layer 250 which is formed by infiltrating molten metalinto the porous ceramic of the dielectric 115 and base 175. During theinfiltration process, the molten metal reacts with the ceramic materialto form an interfacial reaction layer that forms the bond layer 250. Itis believed that the reaction layer is confined to a zone near theircontact surfaces and penetrates less than about 250 μm into each porousceramic surface to provide a bond layer 250 having a thickness of fromabout 50 to about 500 μm. This method of joining the electrostaticmember 100 to the base 175 provides a strong, vacuum tight, bond layer250 that is also substantially free of voids and provides uniformthermal transfer rates across the interface between the base 175 and theelectrostatic member 100. Furthermore, infiltration of molten metal intothe porous ceramic provides a relatively thin bond layer 250 thatminimizes bowing of the electrostatic member 100 which would otherwisewarp the receiving surface 120 and render the electrostatic chuck 55unusable.

[0058] In another version, the base 175 and the electrostatic member 100are joined together by brazing. By brazing it is meant bonding of aceramic member to another ceramic or metal member, using an alloy havinga melting point lower than either of the members being joined. In onemethod, a thin sheet of brazing metal (not shown) is placed between theelectrostatic member 100 and the base 175. The assembled electrostaticmember 100 and base 175 is heated to allow the metal to react withsurfaces of the electrostatic member 100 and the base 175 to form thestrong ductile bond layer 250. Alternatively, the brazing metal can bedeposited directly on the surfaces to be joined and the assembledelectrostatic member 100 and base 175 heated to form the bond layer 250.The brazing metal can comprise aluminum, zinc, copper, silicon, oralloys thereof. The assembled electrostatic member 100 and base 175 areheated to a temperature sufficiently high to melt the brazing metal, butless than the temperatures that would cause softening of theelectrostatic member 100 and base 175. Generally, the electrostaticmember 100 and base 175 are heated to a temperature of up to about 600°C. for about 180 seconds to form the brazed bond layer 250.

[0059] Heater

[0060] In another aspect of the present invention, the electrostaticchuck 55 comprises a heater 235 positioned below and abutting thedielectric 115 of the electrostatic member 100 to heat the substrate 30.The dielectric 115 diffuses the heat from the heater 235 and therebyprovides more uniform temperatures across the substrate 30. Also, theability of the ceramic material of the dielectric 115 to withstand hightemperatures allows the heater 235 to be operated at more elevatedtemperatures than that obtainable with an electrostatic chuck 55 havinga polymer dielectric. A preferred heater 235 comprises a resistiveheating element 255 that has a resistance sufficiently high to raise thetemperature of the substrate 30 by at least about 100° C. The resistiveheating element 255 can be made from tungsten, molybdenum, iron, nickel,copper, Inconel or alloys thereof. Preferably, the resistive heatingelement 255 comprises a planar shape that is sized to match the size ofthe substrate 30 to provide a heat flux that is relatively uniformacross the entire backside of the substrate 30. The resistive heatingelement 255 can be shaped as a flat coil wound in a spiral or whirl, awire mesh, or a zig-zag shaped element. A heater power supply 260 iselectrically connected to the resistive heating element 255 to power theheater 235. The resistive heating element 255 is electrically connectedto the heater power supply 260 by heater connectors 270 a,b thatcomprise a refractory metal and are bonded to the resistive heatingelement 255 by infiltration of a metal having a relatively low meltingtemperature. The heater power supply 260 comprises a source which has apower output of from about 500 to about 3500 watts, and which can beadjusted to provide a current level that achieves a desired substratetemperature. Preferably, a temperature controller 275 is provided tomonitor the substrate temperature and adjust the output of the heater235 to maintain the substrate 30 at temperatures from about 25 to about500° C.

[0061] Preferably, the heater 235 is embedded in the base 175 ratherthan in the dielectric 115 of the electrostatic member 100. Prior artchucks that have a heater embedded in a ceramic dielectric often crackfrom the high thermal stresses generated by localized expansion of theceramic material surrounding the heater 235. In contrast, placing theheater 235 below the ceramic dielectric 115 or inside the base 175 heatsthe base 175 which uniformly heats the dielectric 115 by conductionwithout causing excessive thermal stresses in the dielectric 115. Also,the embedded heater 235 can maintain the substrate 30 in a small rangeof temperatures with more accuracy and stability than that obtained byradiative heating, because the thermal mass of the base 175 and thedielectric 115 serve as heat sinks that prevent localized temperaturefluctuations from excessively changing the temperature of the substrate30.

[0062] The substrate 30 is heated by powering the resistive heatingelement 255 of the heater 235 by the heater power supply 260. A powerlevel of the current provided by the heater power supply 260 is adjustedby the temperature controller 275 in relation to a measured temperatureof the substrate 30 to raise the substrate 30 to a temperature suitablefor processing the substrate 30. The base 175 can reduce the flow ofheat from the electrostatic chuck 55 to the support 190 or the surface50 of the chamber 25. Optionally, heat is removed from a support 190below the base 175 by circulating a heat transfer fluid through thechannels 230 in the support 190. During processing, the temperature ofthe substrate 30 is monitored using a temperature sensor 285, such as athermocouple embedded in the receiving surface 120 that provides asignal to the temperature controller 275 that controls the heater 235 tomaintain the substrate 30 within the desired narrow temperature range.Preferably, the electrostatic chuck 55 of the present invention is ableto maintain the substrate 30 at a temperature of from about 25 to about500° C. within a range of about ±10° C., and more preferably, within arange of about ±5° C.

[0063] Support

[0064] The support 190 serves to secure the electrostatic chuck 55 tothe chamber 25, and also perform one or more of other functions, such asreduce thermal expansion stresses between the chuck 55, base 175, andchamber 25; serve as a thermal insulator or thermal conductor dependingupon the desired temperature of the substrate 30; and also control heattransfer rates between the substrate 30 and the chamber 25.

[0065] One version of the support 190 is adapted to reduce thermalexpansion stresses between the chuck 55, base 175, and the surface 50 ofthe chamber 25. In this version, the support 190 is fabricated from amaterial having a coefficient of thermal expansion that is within about±30% of a coefficient of thermal expansion of the base 175. Morepreferably, the support 190 comprises a coefficient of thermal expansionof from about 2 to about 27 ppm/° C. and most preferably of from about 3to about 12 ppm/° C. The support 190 comprises a ceramic, metal, orcomposite or mixture of ceramic and metal, including by way of example,one or more of aluminum oxide, aluminum nitride, boron carbide, carbon,cordierite, mullite, silicon carbide, silicon nitride, silicon dioxide,zirconium oxide, aluminum, copper, molybdenum, titanium, tungsten,zirconium and mixtures thereof. For example, a suitable support 190 formatching the thermal expansion coefficient of a base 175 comprising acomposite of aluminum and silicon carbide (AlSiC) (which has a CTE offrom about 4 to about 10 ppm/° C.) comprises zirconium (which has a CTEof about 6 ppm/° C.).

[0066] In another version, the support 190 is bonded to the base 175 ofthe electrostatic chuck 55 by a second bond layer 295 of compliant andductile material that is provided to further absorb the thermal stressesthat occur from differences in thermal expansion of the support 190 andthe base 175. The bond layer 295 also generally has a thickness of fromabout 50 to about 500 μm. The bond layer 295 is made from a metal suchas aluminum, copper, iron, molybdenum, titanium, tungsten or alloysthereof. In addition, the bond layer 295 provides an interface with amore homogeneous composition and more uniform heat transfer rates to andfrom the substrate 30. The bond layer 295 also reduces the differencesin thermal impedances that occur at the interface between the base 175and the electrostatic member 100.

[0067] Referring to FIGS. 7a to 7 c, in another version, the support 190is adapted to thermally insulate the base 175 of the electrostatic chuck55 from the surface 50 of the chamber 25. In this version, the support190 comprises a cavity 300 that is shaped and sized to serve as athermal barrier that insulates the electrostatic chuck 55 from thesurface 50 of the chamber 25. The cavity 300 is shaped and sized toprovide a temperature differential that is sufficient to enable theelectrostatic chuck 55 to be sealed to the surface 50 by a conventionallow temperature vacuum seal, such as an O-ring 240. As explained above,high temperatures can cause the polymer O-ring 240 to lose itsresilience and therefore its ability to form a seal. Preferably, thesupport 190 with the cavity 300 comprises a thermal conductivity of lessthan about 6 W/mK to control heat transfer rates from the electrostaticchuck 55. More preferably, the support 190 comprises a cavity 300 havinga cross-sectional area that is shaped and sized to provide a temperaturedifferential of at least about 100° C. between the chuck 55 and thesurface 50 of the chamber 25 when the substrate 30 is held at atemperature of about 500° C.

[0068] Referring to FIG. 7a, the cavity 300 comprises a cross-sectionhaving dimensions only slightly smaller than and corresponding to thoseof the support 190. Alternatively, the cavity 300 can comprise a morecomplex shape tailored to control the rate at which heat is removed fromdifferent portions of the base 175 to provide more uniform temperaturesacross the receiving surface 120 of the electrostatic chuck 55. Forexample, as shown in FIG. 7b, the cavity 300 can also comprise atrapezoidal cross-section to increase heat removal from the peripheraledge of the electrostatic chuck 55, when the peripheral edge issubjected to a higher heat load from the energized process gas. Inanother alternative, shown in FIG. 7c, the cavity 300 comprise anannular channel having a rectangular cross-section which allows moreheat to be removed from the center of the base 175 thereby compensatingfor a greater heat flux at the center of the electrostatic chuck 55.

[0069] Referring to FIG. 7c, the cavity 300 can further comprise a gasinlet 310 a and a gas outlet 310 b for supplying and removing a gas,such as helium, argon, nitrogen, or air to the cavity 300. By varyingthe pressure of the gas in the cavity 300, the amount of heat conductedfrom the substrate 30 through the support 190 can also be varied. Thepressure of the gas in the cavity 300 is regulated to maintainsubstantially uniform temperatures across the receiving surface 120 ofthe chuck 55. Typically, the pressure of the gas is less than about 50mTorr, and more preferably, the pressure of the gas is from about 2 toabout 50 mTorr.

[0070] Optionally, as illustrated in FIG. 6, the support 190 cancomprise threaded inserts 315 of a low thermal expansion alloy, such asKovar™ or Invar™, into which bolts 320 are threaded to secure thesupport 190 (with the electrostatic chuck 55 bonded thereto) to thechamber 15. The threaded inserts 315 provide greater resilience andcompliance than the brittle material of a ceramic support 190 and aremore easily machined to provide threads for receiving the bolts 320.Alternatively, the support 190 is secured in the chamber 25 by aclamping ring 325, as shown in FIG. 1. The clamping ring 325 allowsmovement due to differences in thermal expansion of the support 190 andthe surface 50 of the chamber 25, thereby preventing warping or crackingof the support 190 and improving the reliability of the vacuum sealbetween the support 190 and the surface 50. Also, any mechanicalstresses induced by conventional mounting bolts made of metal arereduced, thereby extending the operating life of the electrostatic chuck55 and support 190. In yet another embodiment, shown in FIGS. 7a to 7 c,one or more of the clamping ring 325, the base 175, or the support 190comprise a curved surface 330 which further reduces the mechanicalstresses on the electrostatic chuck 55 and the support 190 bydistributing a clamping force over a larger area.

[0071] Method of Fabrication

[0072] In another aspect, the present invention is directed to a methodof fabricating an electrostatic chuck 55 comprising an electrostaticmember 100 having an electrode 105 covered by a dielectric 115, a base175 joined to the electrostatic member 100, and, optionally, a heater235. A preferred method of fabricating the electrostatic chuck 55 willnow be described; however, other methods of fabrication can be used toform the electrostatic chuck 55 and the present invention should not belimited to the illustrative methods described herein.

[0073] Forming the Electrostatic Member

[0074] The dielectric 115 of the electrostatic member 100 comprises aceramic or polymer material. Suitable high temperature materials includeceramics such as for example, one or more of aluminum oxide, aluminumnitride, silicon nitride, silicon dioxide, titanium dioxide, zirconiumoxide, or mixtures thereof. Generally, aluminum nitride is preferred forits high thermal conductivity which provides high heat transfer ratesfrom the substrate 30 to the electrostatic chuck 55. Also, aluminumnitride has a low CTE of about 5.5 ppm/° C. which closely matches a CTEof an electrode 105 made of molybdenum which has a CTE of about 5.1ppm/° C. Also, aluminum nitride exhibits good chemical resistance inerosive environments, especially halogen containing plasma environments.The dielectric 115 is formed by freeze casting, injection molding,pressure-forming, thermal spraying, or sintering a ceramic block withthe electrode 105 embedded therein. Preferably, a ceramic powder isformed into a coherent mass in a pressure forming process by applicationof a high pressure and a temperature. Suitable pressure formingapparatuses include an autoclave, a platen press, or an isostatic press,as for example, described in U.S. patent application Ser. No. 08/965,690filed Nov. 6, 1997; which is incorporated herein by reference.

[0075] The electrode 105 of the electrostatic member 100 comprises arefractory metal capable of withstanding high temperatures, such astemperatures of at least about 1500° C. Suitable metals include, forexample, tungsten, molybdenum, titanium, nickel, tantalum, molybdenum oralloys thereof. Preferably, the electrode 105 is made of molybdenum,which has a thermal conductivity of about 138 W/mK, which issubstantially higher than that of most metals and alloys commonly usedfor electrodes 105 and enhances heat transfer rates through theelectrostatic member 100. In the embodiment shown in FIG. 6, theelectrode 105 comprises a thin mesh which is embedded in the dielectric115 and is shaped and sized depending upon the shape and size of thesubstrate 30.

[0076] In a preferred method of forming an electrostatic member 100 withan embedded electrode 105, an isostatic press is used to apply a uniformpressure over the entire surface of the electrostatic member (notshown). A typical isostatic press comprises a pressure resistant steelchamber having a pressurized fluid for applying a pressure on anisostatic molding bag. A powdered precursor comprising a suitableceramic compound mixed with an organic binder, such as polyvinylalcohol, is packed around the electrode 105 in the isostatic molding bagand the bag is inserted in the isostatic press. The fluid in thepressure chamber is pressurized to apply a pressure on the ceramicmaterial. It is desirable to simultaneously remove air trapped in theisostatic molding bag using a vacuum pump to increase the cohesion ofthe powdered precursor. The unitary ceramic preform comprising adielectric 115 having an electrode 105 therein is removed from themolding bag and sintered to form an electrostatic member 100 with anembedded electrode 105. The gas flow conduits 130 are subsequentlyformed in the electrostatic member 100 by drilling, boring, or milling;or they can be formed by placing suitable inserts in the ceramic preformduring the molding process. After the electrostatic member 100 isformed, the receiving surface 120 is ground to obtain a flat surface toefficiently thermally couple the substrate 30 to the electrostaticchuck.

[0077] The electrical connector 140 is electrically connected to theelectrode 105 of the electrostatic chuck 55 to conduct an electricalcharge to the electrode 105 from a voltage supply terminal 340 in thechamber 25. The electrical connector 140 is also made of a refractorymetal having a melting temperature of at least about 1500° C. Suitablemetals include, for example, tungsten, titanium, nickel, tantalum,molybdenum or alloys thereof. The electrical connector 140 comprises arod or plug 345 having a length sufficiently long to extend from thevoltage supply terminal 340, through a hole 350 in the dielectric 115and the support 190, to electrically engage the electrode 105. Otherequivalent structures for the electrical connector 140 includerectangular leads, contact posts, and laminated conducting structures.

[0078] In a preferred structure, shown in FIG. 6, the plug 345 of theelectrical connector 140 is bonded to the electrode 105 by a conductingmaterial in a liquid phase. Preferably, the conducting liquid phasecomprises a metal having a softening temperature of less than about1500° C., and more preferably, less than about 600° C. Suitablematerials include aluminum, copper, iron, molybdenum, titanium, tungstenor alloys thereof. The electrical connector 140 is aligned in the hole350 to provide a gap 355 sufficiently large to allow the conductingliquid phase to infiltrate between and electrically connect the plug 345to the electrode 105. The more ductile conducting material that fillsthe gap 355 also absorbs thermal stresses arising from the verticalexpansion of the electrical connector 140 relative to other surroundingstructures, such as the electrostatic member 100. The volume of gap 355in which the metal is infiltrated is sufficiently large to enable themetal to substantially fill the space between the electrical connector140 and the electrode 105 to provide a good electrical connection.However, it has been discovered that reducing the volume of gap 355 intowhich the metal is infiltrated serves to significantly reduce crackingof the ceramic material surrounding the electrical connector 140 and canalso reduce bowing of the electrostatic member 100. In the embodimentshown in FIG. 6, the gap 355 is defined by a bore 365 in the dielectric115, the bore 365 having a first diameter that is smaller than the outerdiameter of the plug 345 of the electrical connector 140, and a seconddiameter larger than the diameter of the plug 345 to allow it to passthrough. A shoulder 370 defined by the first and second diameters of thebore 365 serves as a stop that prevents the electrical connector 140from contacting the electrode 105, thereby forming a gap 355therebetween that can be infiltrated by molten or softened metal (whichis later solidified) to electrically connect the plug 345 to theelectrode 105. Thus, the electrical connector 140 is not joined directlyto the electrode 105 but instead is electrically coupled via the gap 355filled with a metal which can readily deform and absorb thermalexpansion and other mechanical stresses. This joint provides a morereliable electrical connection between the electrical connector 140 andthe electrode 105.

[0079] Alternatively, the electrical connector 140 can be electricallyconnected to the electrode 105 by a brazed connection. Referring toFIGS. 8a and 8 b, a metal insert 375 is placed between the plug 345 andthe shoulder 370 of the bore 365. The electrostatic chuck 55 and theplug 345 are then heated causing the metal insert 375 to soften and fillthe gap 355. Typically, the electrostatic chuck 55 and the plug 345 aremaintained at a temperature of about 600° C. for at least about 180seconds. Thereafter, they are cooled to solidify the metal in the gap355 to form a brazed connection between the electrical connectors 140and the electrode 105 as shown in FIG. 8b. Optionally, a pressure can beapplied to the plug 345 of the electrical connector 140 while heatingthe electrostatic chuck 55 to cause the softened metal from the metalinsert 375 to infiltrated and fill the gap 355.

[0080] Optionally, as shown in FIG. 6, tubes 380 of a ceramic material,such as aluminum oxide, extend through one or more of the dielectric115, the support 190 and the base 175. These tubes 380 serve toelectrically isolate electrical connector 140 and the heater connectors270 a,b from the bond layers 250, 295, the base 175, and the support190. They also align the conduit 130 and holes 165 a,b through which thelift pins 160 pass to prevent the formation of a plasma glow dischargetherein during operation of the electrostatic chuck 55. The tubes 380comprise an outer diameter that allows them to be held in placesubstantially without the use of an adhesive. Preferably, the tubes 380surrounding the electrical connector 140 and the heater connector 270a,b comprise an inner dimension and a shape that conforms to theconnectors 140, 270 a,b. More preferably, the tubes 380 surrounding theconduits comprise an inner diameter sufficiently small to prevent plasmaformation in the conduit 130 and in the lift pin holes 165 a,b.

[0081] Forming the Base

[0082] The version of the base 175 supporting the electrostatic member100 which comprises porous ceramic infiltrated with metal is fabricatedby forming a ceramic preform (not shown) and infiltrating a liquid ormolten metal into the ceramic. The ceramic preform is made from aceramic powder having an average particle size that provides the desiredvolume of porosity in the ceramic preform. The average particle size ofthe ceramic powder can be obtained by milling processes, such as ballmilling or attrition milling. The total porosity can be furtherincreased or decreased using agglomerated powder comprising particles ofvarious sizes. Although the desired pore size varies depending on theceramic being infiltrated, it is generally desirable that the ceramicpowder have an average particle size of from about 0.1 to about 50 μm,to yield a volume porosity of from about 20 to about 80 volume %.

[0083] The version of the base 175 supporting the electrostatic member100 comprising an embedded heater 235 is formed by placing the resistiveheating element 255 in a mold (not shown), packing the mold with ceramicpowder, and applying a pressure of from about 48 MPa to about 69 MPa tothe mold to form the preform. The pressure applied to the ceramic powdercan be applied using an autoclave, a platen press, or an isostaticpress. Preferably, an isostatic press is used to apply a uniformpressure over the entire surface of the mold to form a ceramic preformhaving high strength. In isostatic pressing, additives such as polyvinylalcohol, plasticizers such as polyethylene glycol, and lubricants suchas aluminum stearate are mixed with the ceramic powder to improve themechanical strength of the preform. Because the preform has sufficientstrength, voids for connectors 140, 270 a,b to the electrode 105 and theresistive heating element 255, the conduit 130 for the heat transfergas, and the holes 165 a,b for the lift pins 160 can be formed usingconventional machining techniques such as drilling, boring, or millingwhile the ceramic preform is in the green state.

[0084] The green preform is sintered to obtain a ceramic preform withthe optional resistive heating element 255 embedded therein. In thesintering process, the green preform is heated in the presence of a gasat a high partial pressure in order to control the total porosity andaverage pore size of the sintered body. Preferably, the partial pressureof the gas is from about 1 to about 10 atmospheres. If binders or otherorganic materials are used in the preform forming process, theseadditives are burned out in the sintering step. In the sinteringprocess, the green preform is placed in a furnace and slowly heated to atemperature of from about 300 to about 1200° C. in a flowing gas such asnitrogen to volatilize the organic materials to form a dense ceramic.

[0085] The second step of forming the base 175 involves an infiltrationprocess. After a ceramic having the desired total porosity and pore sizeis obtained, a liquid phase of metal or molten metal is infiltrated intothe voids or pores of the ceramic. The infiltration can be accomplishedby any suitable process including, for example, a method in which moltenmetal is brought into contact with a ceramic and infiltrates into theinterconnecting pores of the ceramic by capillary action. In a preferredmethod, infiltration is accomplished in a pressure vessel using apressure infiltration process. In this method, the ceramic is placed inthe pressure vessel with metal around it, and the vessel evacuated andheated to remove air from the pores of the ceramic. Once the pressurevessel is evacuated, the ceramic and surrounding metal are heated to atemperature corresponding to the softening temperature of the metal tobe infiltrated. The molten metal is introduced into the pressure vesselunder pressure to fill substantially all voids, cavities and pores inthe ceramic. For example, in the embodiment wherein the ceramiccomprises silicon carbide having a porosity of about 30%, theinfiltration of molten aluminum is accomplished by maintaining thepressure vessel at a pressure of about 1030 kPa (150 psi), and atemperature of at least 600° C. for about 180 seconds.

[0086] Forming the Bond Layers

[0087] The base 175 is then bonded to the ceramic dielectric 115 of theelectrostatic member 100 by the infiltration process described above. Ina preferred embodiment, the electrostatic member 100 is placed on top ofthe base 175 in a pressure vessel and molten metal or alloy is broughtinto contact with the assembly. Typically, the process vessel ismaintained at a pressure of from about 690 kPa (100 psi) to about 1380kPa (200 psi), and the molten metal is maintained at temperature of fromabout 600 to about 700° C. for at least about 180 seconds. During theinfiltration process, molten metal reacts with the ceramic dielectric115, forming an intermetallic bond layer 250 between the electrostaticmember 100 and the base 175. After infiltration, the assembledelectrostatic chuck 55 is cooled to solidify the metal to form the bondlayer 250. It has been found that a substantially void-free andcrack-free bond between the electrostatic member 100 and the base 175can be achieved by controlling the rate at which the electrostatic chuckassembly is cooled. Preferably, the electrostatic chuck assembly iscooled at a rate of from about 10 to about 1° C./hr.

[0088] In an alternative method, the base 175 is formed and bonded tothe electrostatic member 100 in a single step. In this method, theelectrostatic member 100 with the electrode 105 is placed on thesintered preform of the base 175 in a pressure vessel. Once the pressurevessel has been completely evacuated, a molten metal is introduced intothe vessel under pressure to substantially fill surface voids, cavitiesand pores in the preform to form a base 175 and to also infiltrate intothe interface and bond the base 175 to the electrostatic member 100.

[0089] In another embodiment, the support 190 is also bonded to thelower surface of the base 175 by the infiltration process. As describedabove, the support 190 can comprise a ceramic or metal structure that isshaped to correspond to the shape of the base 175. The support 190 canbe formed by a variety of methods, including for example, casting,isostatic pressing, or machining a block of metal or sintered ceramicmaterial. The cavity 300 is formed in the base 175 by drilling, boring,or milling. For example, in a preferred embodiment shown in FIG. 7c, thesupport 190 is formed from two pieces of cast zirconium. A top member190 a comprises a right cylinder having a cavity 300 with an annularchannel therein, and a lower plate 190 b that covers the cavity 300.Optionally, the lower plate 190 b can also be machined to provide thegas inlet 310 a and the gas outlet 310 b for supplying and exhaustingheat transfer gas from the cavity 300 respectively. After forming thecavity 300, the top and bottom surfaces of the assembled support 190 areground until the surface roughness of the support 190 is less than about1 micron. Surface grinding is needed for the support 190 to uniformlycontact the base 175 and to provide a strong and substantially void freebond layer 295 between the support 190 and the base 175. A smooth bottomsurface is useful to enhance the vacuum seal between the support 190 andthe bottom surface 50 of the chamber 25. After grinding, the support 190is thoroughly cleaned to remove grinding debris. For those embodimentsin which the support 190 comprises a metal, the exposed surfaces of thesupport 190 can be treated or coated with a material to reduce erosionor corrosion by the energized process gases. For example, the exposedsurfaces of the support 190 can be anodized or coated with thermallysprayed alumina.

[0090] The following examples illustrate the thermal expansioncompatibility of a variety of combinations of materials that can be usedto form the electrostatic chuck 55, the base 175 and the support 190, orfor bonding the electrostatic member 100 to a base 175 by the bond layer250. The test coupons are scaled down to approximate the dimensions ofan electrostatic chuck 55 and are made from the different materialsbonded together by the infiltration process of the present invention.The silicon carbide and mullite materials were high porosity materialsinfiltrated with a compliant metal, such as aluminum. In theinfiltration process, molten aluminum was infiltrated in a heated andpressurized vessel at a pressure of about 1030 kPa (150 psi) and atemperature of about 600° C.

[0091] In Examples 1 to 9, the surface flatness of the bonded testcoupons was measured using a profilemeter to determine the degree anddirection of bowing which measures the curvature of a surface from thecenter to a peripheral edge occurring due to a thermal expansionmismatch of two different materials bonded together. Positive bowingoccurs when the center of a surface is higher relative to the peripheraledge, and negative bowing occurs when the peripheral edge is higher. Itis desirable for the receiving surface 120 of the electrostatic chuck 55to be flat to prevent breaking of a substrate held to the surface, andto reduce any non-uniformity in the heat transfer rates which occurswhen one portion of the substrate 30 is closer to the electrostaticchuck 55 or to the source of the energized process gas. For example, asurface 120 having a diameter of about 200 mm should exhibit less thanabout 254 wm (10 mils) of bowing. Excessive bowing can also cause thedielectric 115, base 175, support 190, or the bond layers 250, 295between them to crack reduce the operating life of the electrostaticchuck 55, or contaminate the chamber 25.

[0092] Referring to Table II, bonded test coupons sized 100 by 180 mmand having a thickness of 10 to 12 mm were repeatedly cycled betweenroom temperature and a temperature of 300° C. or higher. Subsequenttesting and examination demonstrate the ability of the metal-ceramiccomposite and the bond of the present invention to securely bonddifferent materials with an acceptable level of bowing andmicrocracking. TABLE II EXAMPLE MATERIALS CTE NO. BONDED MISMATCHBONDING QUALITY 1 AlSiC to AlN 6.9 to 5.5 Excellent/positive bowing ofless than about 10 mils. 2 AlSiC to Al₂O₃ 6.9 to 7.1 Excellent/positivebowing of less than about 6 mils. 3 AlSiC to Mullite 6.9 to 7.9Excellent/No bowing, Mullite cracking 4 AlSiC to Ti alloys 6.9 to 9.5Excellent/positive bowing 5 AlSiC to AlSiC 6.9 to 6.9 Excellent/Nobowing 6 AlSiC to Metal 6.9 to 6.0 Excellent/No bowing (Mo, Ta, W, Kovarand Invar) 7 Al—SiSiC to AlN 5.8 to 5.5 Excellent/positive bowing ofless than about 2 mils. 8 AlC to AlN 4.8 to 5.5 Excellent/negativebowing of less than about 3 mils. 9 AlC to AlC 4.8 to 4.8 Excellent/Nobowing

[0093] In this manner, the present invention provides a system forholding and supporting a substrate 30 that is capable of maintaining thesubstrate 30 in a narrow range of high temperatures. The substrate 30 isheated or cooled depending on the heat provided by the plasma and theoptional heater 235. In addition, the electrostatic chuck 55, base 175,and support 190 can rapidly heat or cool the substrate 30 withoutfracturing or microcracking from thermal shock or thermal expansionstresses. Also, the present invention provides a reliable electricalconnection between the electrical connector 140 and the electrode 105 ofthe electrostatic chuck 55.

[0094] Although the present invention has been described in considerabledetail with regard to certain preferred versions thereof, other versionsare possible. For example, the electrostatic chuck can be used to holdother substrates, such as flat panel displays, circuit boards, andliquid crystal displays as apparent to those skilled in the art andwithout deviating from the scope of the invention. Also, theelectrostatic chuck of the present invention can be used in otherenvironments, such as physical vapor deposition and chemical vapordeposition chambers. Therefore, the appended claims should not belimited to the description of the preferred versions contained herein.

What is claimed is:
 1. An electrostatic chuck for holding a substrate,the electrostatic chuck comprising: an electrostatic member comprising adielectric covering an electrode that is chargeable to electrostaticallyhold the substrate; and a base bonded to the electrostatic member by abond layer, the base comprising a heater capable of raising thetemperature of a substrate held on the electrostatic member by at leastabout 100° C.
 2. An electrostatic chuck according to claim 1 wherein theheater comprises a resistive heating element.
 3. An electrostatic chuckaccording to claim 1 wherein the bond layer comprises a metal.
 4. Anelectrostatic chuck according to claim 1 wherein the base comprises acomposite of a ceramic and metal, the composite having a coefficient ofthermal expansion within about ±30% of a coefficient of thermalexpansion of the electrostatic member.
 5. An electrostatic chuckaccording to claim 4 wherein the composite comprises porous ceramicinfiltrated with an metal.
 6. An electrostatic chuck according to claim5 wherein the bond layer comprises the same metal as the infiltratedmetal.
 7. A method of fabricating an electrostatic chuck for holding asubstrate, the method comprising the steps of: (a) forming anelectrostatic member comprising a dielectric covering an electrode thatis chargeable to electrostatically hold the substrate; (b) forming abase comprising a heater capable of raising the temperature of asubstrate held on the electrostatic member by at least about 100° C.;and (c) bonding the base to the electrostatic member by a bond layer. 8.A method according to claim 7 wherein (c) comprises infiltrating amolten metal into an interface between the electrostatic member and thebase.
 9. A method according to claim 8 comprising cooling the base andelectrostatic member at a cooling rate of from about 10 to about 100°C./hr.
 10. A method according to claim 7 wherein (c) comprises placing abrazing material between the electrostatic member and base and heatingthe brazing material to a temperature of less than about 600° C. to formthe bond layer.
 11. A method according to claim 7 wherein the bond layercomprises a metal.
 12. A method according to claim 7 further comprisingembedding a heater comprising a resistive heating element in the base.13. A method according to claim 7 comprising forming the base byinfiltrating a metal into porous ceramic.
 14. A method according toclaim 13 wherein the metal also forms the bond layer.
 15. A methodaccording to claim 13 comprising forming the porous ceramic by sinteringone or more of aluminum oxide, aluminum nitride, boron carbide, carbon,cordierite, mullite, silicon carbide, silicon nitride, silicon dioxideand zirconium oxide.
 16. A method according to claim 13 comprisinginfiltrating the porous ceramic with a metal comprising aluminum,copper, iron, molybdenum, titanium, tungsten or alloys thereof.
 17. Anelectrostatic chuck for holding a substrate, the electrostatic chuckcomprising: an electrostatic member comprising a dielectric covering anelectrode that is chargeable to electrostatically hold the substrate;and a base bonded to the electrostatic member by a bond layer, the basecomprising a composite of a ceramic and metal, the composite comprisinga coefficient of thermal expansion within about ±30% of a coefficient ofthermal expansion of the electrostatic member.
 18. An electrostaticchuck according to claim 17 wherein the bond layer comprises a metal.19. An electrostatic chuck according to claim 17 wherein the compositecomprises porous ceramic infiltrated with an metal.
 20. An electrostaticchuck according to claim 19 wherein the bond layer comprises the samemetal as the infiltrated metal.
 21. An electrostatic chuck according toclaim 17 wherein the base comprises a heater capable of raising thetemperature of a substrate held on the electrostatic member by at leastabout 100° C.
 22. An electrostatic chuck according to claim 21 whereinthe heater comprises a resistive heating element.
 23. A method offabricating an electrostatic chuck for holding a substrate, the methodcomprising the steps of: (a) forming an electrostatic member comprisinga dielectric covering an electrode that is chargeable toelectrostatically hold the substrate; (b) forming a base comprising acomposite of a ceramic and metal, the composite comprising a coefficientof thermal expansion within about ±30% of a coefficient of thermalexpansion of the electrostatic member; and (c) bonding the base to theelectrostatic member by a bond layer.
 24. A method according to claim 23wherein (c) comprises infiltrating a molten metal into an interfacebetween the electrostatic member and the base.
 25. A method according toclaim 24 comprising cooling the base and electrostatic member at acooling rate of from about 10 to about 100° C./hr.
 26. A methodaccording to claim 23 wherein (c) comprises placing a brazing materialbetween the electrostatic member and base and heating the brazingmaterial to a temperature of less than about 600° C. to form the bondlayer.
 27. A method according to claim 23 wherein the bond layercomprises a metal.
 28. A method according to claim 23 wherein the basefurther comprises a heater capable of raising the temperature of asubstrate held on the electrostatic member by at least about 100° C. 29.A method according to claim 28 comprising embeddin g a heater comprisinga resistive heating element in the base.
 30. A method according to claim23 comprising forming the base by infiltrating a metal into porousceramic.
 31. A method according to claim 30 wherein the metal also formsthe bond layer.
 32. A method according to claim 30 comprising formingthe porous ceramic by sintering one or more of aluminum oxide, aluminumnitride, boron carbide, carbon, cordierite, mullite, silicon carbide,silicon nitride, silicon dioxide and zirconium oxide.
 33. A methodaccording to claim 30 comprising infiltrating the porous ceramic with ametal comprising aluminum, copper, iron, molybdenum, titanium, tungstenor alloys thereof.